1. Field of the Invention
The present invention relates to a ferrite composition and a process of production thereof.
2. Description of the Related Art
Mnxe2x80x94Zn ferrite components, Nixe2x80x94Cuxe2x80x94Zn ferrite components, Mnxe2x80x94Mgxe2x80x94Zn ferrite components, and other magnetic ferrite compositions are made broad use of for various types of electronic apparatuses as for example magnetic cores for coils, transformers, magnetic heads, etc.
Along with the recent reduction in size and reduction in thickness of electronic apparatuses, a similar reduction in size and reduction in thickness of the magnetic ferrite components have become desirable. In order to maintain the reliability of the product along with this, a higher mechanical strength and higher magnetic characteristics are demanded.
From this viewpoint, to improve the mechanical strength, there are known the methods of using a hot press for manufacture, reducing the particle diameter of the raw material powder and lowering the sintering temperature to reduce the crystal particle diameter, or adding various types of additives to reduce the crystal particle diameter. Further, to improve the magnetic characteristics, there are known the methods of adding various types of additives and optimizing the sintering conditions.
With the method of using a hot press to improve the mechanical strength, however, the production time becomes longer and expensive equipment is required, so there are large cost demerits.
Further, with the method of making the raw material powder finer to improve the mechanical strength, a separate process for reducing the particle diameter becomes necessary. Also, the finer raw material powder is extremely difficult to handle when producing a magnetic ferrite component.
Further, with the method of improving the mechanical characteristics by adding various types of additives, there are large cost demerits and balancing the various magnetic characteristics becomes difficult in some cases.
Still further, with the method of improving the magnetic characteristics by optimizing the sintering conditions, control of the sintering atmosphere, temperature raising and lowering rate, etc. becomes difficult, introduction of new equipment becomes necessary in some cases, and other problems arise.
Note that Japanese Unexamined Patent Publication (Kokai) No. 1994-132111 discloses the amount of carbon contained in a ferrite sintered body, but makes no mention at all of the control of the same. Further, the actually included amount of carbon is normally about the same extent as the amount of carbon included in a sintered body obtained by removing the binder and then sintering (about 100 ppm) and it is difficult to secure sufficient mechanical strength. That is, in the above publication, the raw material powder is compacted by cold isostatic pressing and sintered in the state with difficult release of oxygen when the hematite material changes to spinel type ferrite. Therefore, the carbon added to the raw material powder before sintering or the reducing agent breaking down under heating to become carbon has an effect on the magnetic characteristics of the phase after sintering. Further, the above publication makes no mention at all of the effect of the residual carbon on the strength and magnetic characteristics.
An object of the present invention is to solve the above problems in the related art and provide a ferrite composition having a high mechanical strength and superior magnetic characteristics even when reducing the size and reducing the thickness and a process for production of the same.
The present inventors took note of the content of carbon in a magnetic ferrite composition and controlled the same to thereby perfect the present invention. Note that in the present invention, a xe2x80x9cmagnetic ferrite compositionxe2x80x9d is used in the sense including both a ferrite material and ferrite sintered body.
The magnetic ferrite composition according to the present invention is characterized by including at least one of Mg, Ni, Cu, Zn, Mn, and Li and having a content of carbon of less than 96 weight ppm, preferably not more than 91 weight ppm, more preferably not more than 77 weight ppm, particularly preferably not more than 70 weight ppm.
The ferrite composition preferably includes, in addition to Mg, at least one of Cu, Zn, Mn, Ni, and Li. A typical example of this ferrite composition is Mgxe2x80x94Cuxe2x80x94Zn ferrite. In such a ferrite composition, the content of the carbon is preferably over 9.7 weight ppm (more than 9.7 weight ppm), more preferably at least 10 weight ppm, particularly preferably at least 15 weight ppm. Further, in such a ferrite composition, the content of carbon is preferably not more than 91 weight ppm.
The ferrite composition may be a ferrite composition including at least Mn and Zn. A typical example of such a ferrite composition is an Mnxe2x80x94Zn ferrite composition. In such a ferrite composition, the content of carbon is less than 52 weight ppm, preferably not more than 50 weight ppm, more preferably not more than 45 weight ppm. Further, in such a ferrite composition, the content of carbon is preferably over 9.8 weight ppm (more than 9.8 weight ppm), more preferably at least 10 weight ppm, particularly preferably at least 15 weight ppm.
The ferrite composition may further include as an additional component at least one oxide selected from silicon oxide, calcium oxide, tin oxide, titanium oxide, niobium oxide, zirconium oxide, vanadium oxide, molybdenum oxide, bismuth oxide, and tantalum oxide.
Further, the ferrite composition may be a ferrite composition including at least one of Cu, Zn, and Mn in addition to Ni. A typical example of such a ferrite composition is an Nixe2x80x94Cuxe2x80x94Zn ferrite composition. In such a ferrite composition, the content of carbon is less than 67 weight ppm, preferably not more than 60 weight ppm, more preferably not more than 50 weight ppm, particularly preferably not more than 45 weight ppm. Further, in such a ferrite composition, the content of carbon is preferably over 9.7 weight ppm (more than 9.7 weight ppm), more preferably at least 10 weight ppm, particularly preferably at least 15 weight ppm.
The process of production of a magnetic ferrite composition according to the present invention controls a flow rate of gas blown into the sintering furnace so as to control the amount of carbon contained in the ferrite composition.
Further, the method of adjusting the bending strength of the magnetic ferrite composition according to the present invention controls the content of the carbon contained in the magnetic ferrite composition.
In the present invention, by controlling the content of the carbon in the magnetic ferrite composition, it is possible to improve the mechanical strength of the magnetic ferrite composition (for example, to give a bending strength of preferably at least 8 kgf/mm2, more preferably at least 10 kgf/mm2) and to provide a highly reliable ferrite composition with little cracking or chipping.
In the present invention, by controlling the content of the carbon in the magnetic ferrite composition to within a predetermined range, it is possible to improve the bending strength while maintaining a high magnetic permeability xcexc in a magnetic ferrite composition of a predetermined composition. Further, in a magnetic ferrite composition of another composition, it is possible to improve the bending strength while maintaining a low core loss.
Note that the carbon contained in the ferrite composition after sintering is considered to be the carbon component contained in the carbonate material and/or organic binder.
The ferrite composition according to the present invention may be used as the core of an inductor, transformer, coil, etc. used in an electronic apparatus such as a radio, television, communications apparatus, office automation apparatus, and switching power source or a magnetic head core used in an electronic apparatus such as a video apparatus or magnetic disk drive or other electronic components.
Among these, the Mgxe2x80x94Cuxe2x80x94Zn ferrite composition and Nixe2x80x94Cuxe2x80x94Zn ferrite composition according to the present invention may be preferably used for inductors, while the Mnxe2x80x94Zn ferrite composition may be preferably used for transformers.
In the process of production of a ferrite composition according to the present invention, when producing the ferrite sintered body, it is possible to blow a gas into the sintering furnace at the time of sintering by a predetermined flow rate and skip the carbon component included in the granulated material to control the amount of carbon after sintering. Therefore, it is easy to balance the mechanical strength and the magnetic characteristics of the obtained ferrite sintered body.
The method of adjusting the bending strength of the ferrite sintered body according to the present invention can control the bending strength of the ferrite sintered body obtained by controlling the amount of carbon in the composition. This new discovery was made by the present inventors.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 1999-264775, filed on September 20, the disclosure of which is expressly incorporated herein by reference in its entirety.